How to divide a Pneumatic Conveying Stream

Pneumatic Conveying Lines

How to divide a Pneumatic Conveying Stream

Splitter for continuous distribution of bulk solid material during pneumatic conveyance - dimensioning, calculation, operating behaviour. Worldwide, a great number of so-called splitters are in operation as elements of pneumatic conveying lines, in order to continuously distribute the conveyed bulk material to several receiving stations. These splitters have taken an important position within the pneumatic conveying systems and are applied in different designs. But there is not much literature available dealing with the phenomenon “splitter”, and providing assistance regarding application possibilities, dimensioning, selection and experiences during operation. The available literature mostly deals with answers to specific questions, like for example pressure losses in various ramifications, etc.
(ed. wgeisler - 31/5/2017)
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Fig. 1: Splitters distribute pneumatic conveying streams to numerous outlets.

The present article intends to close this gap and to provide an overview over the possible applications and typical configurations of splitters, with their advantages and disadvantages. Furthermore various selection criteria for usage of splitters are introduced and discussed. In addition, dimensioning and operation of splitters are discussed. Possible susceptibilities to interferences are pointed out and measures to ensure or promote a smooth operation as well as operation experiences with splitter systems are introduced.

1   Splitters – Definition and Limitation for further Discussion

The term “splitter” stands for a multitude of process technologies in the bulk material industry. They all have in common that they are used to evenly distribute a material flow and to simultaneously lead it to several target locations. This can be done both within a mechanical conveyor section, e.g. with a special spreading auger and injectors (see Fig. 1), as well as through a constructive element (the splitter) in a pneumatic conveyor section. An alternating distribution is given if only one particular target location out of several other possible locations is to be reached (e.g. with the help of a pipe branching). In case all possible target locations are to be fed, we speak of an even distribution. This article deals with the even and simultaneous distribution of particles, in which a conveying gas (usually air) serves as a pneumatic carrier medium.

Splitters are mostly used in engineering plants, such as for the treatment of flue gas, where a sorbent is evenly blown into a flue gas channel in up to 16 different locations. A further application is dust firing in coal power plants, in which an even coating of the blown-in dust and air mixtures over the cross section of the boiler are an important precondition for an optimal and low-emission combustion.

If no splitters are applied in these cases, a separate conveyor track is needed for each single air injection point, together with a conveyor- and dosing unit and possibly with air supply (see Fig 2a). Apart from spacial problems, this leads to a multiplication of costs.

An initial saving in costs can be achieved through a downstream splitter, with which the total amount of air is divided onto the individual conveyor tracks and metering points respectively. Hereby the distribution (of air) can be done as an equilibrium distribution (Fig. 2b) or through the application of device/venture nozzles as forced distribution (Fig. 2c).

Fig. 2: Splitters in pneumatic conveying applications:    a) individual supply;    b) air splitter (equilibrium distribution);    c) air splitter (forced
distribution);    d) dilute phase splitter;    e) dilute phase splitter with additional air function;    f) dense phase splitter                    

Significant savings can be achieved if the splitter is arranged delivery sided with an optimal arrangement close to the injection locations (Fig. 2d). In this case the air supply, dosage organ, conveying organ and a section of the conveying line are only single executed. While feeding against higher pressures or at dense phase conveying, the distribution could also be realized in the conveyor mechanism (Fig. 2f).

The splitters discussed in this article are splitters for a distribution within a pneumatic conveying section as a distributing conveyor organ (e.g. in Figs. 2d/2e) or as a branching organ in the conveyor line (like for example in Fig. 2f).

1.1  Splitter Designs

Based on material characteristics, conveying tasks and conveying types (dilute phase/dense phase) there are multiple designs of splitters. Not all of them are well thought through or suitable for each and every case. For example the distribution can be done from a fluidized bed, the splitter can be streamed through from up to down or vice versa, and there are also horizontal splitters. As an example, so-called riffle boxes, which are used for the distribution of coal dust to (mostly 4-6) burners in coal-fired power plants are well known (Fig. 3). Rotating splitters have also been and are still used for the distribution of a mass flow. However, the most used are the dilute phase stream splitters with various distribution mechanisms, which are streamed through from bottom to top. (Figs. 4, 5)

Fig. 3: Coal dust riffle box [2]                                                                                          

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